Stainless steel and articles



United States Patent 3,282,686 STAINLESS STEEL AND ARTICLES Paul M. Allen, Middletown, Ohio, assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio No Drawing. Filed Feb. 1, 1965, Ser. No. 429,656 7 Claims. (Cl. 75125) My application is a companion of my copending application, Ser. No. 299,110 filed July 31, 1963, and entitled, Stainless Steel and Articles, and the invention relates to stainless and more especially to a stainless steel suited to a variety of indoor and outdoor applications.

One of the objects of my invention is the provision of a stainless steel which is comparatively inexpensive in that it employes a minimum of expensive alloying ingredients; which steel readily lends itself to hot-working and then to cold-working at minimum cost in that it possesses a low work-hardening rate and permits maximum coldreduction without necessity for intermediate anneal; and which cold-worked steel readily lends itself to a variety of forming and fabricating operations.

Another object is the provision of hot-rolled sheet, strip, wire and like products as well as the provision of cold-rolled sheet and strip of cold-drawn wire and the like, all at minimum cold-working costs; which coldrolled sheet, strip, wire and like products, as well as hotrolled products where desired, lend themselves to a variety of forming and fabricating operations such as bending, drawing, deep-drawing, spinning, and the like, as well as shearing, cutting, sawing and drilling; and which products readily may be brazed and welded as in the fabrication of a host of articles of ultimate use.

A further object is the provision of a variety of stainless steel articles of ultimate indoor use such as kitchen sinks, trim fittings, and the like, having eye appeal yet being adapted to withstand the corrosive action of foodstutfs commonly encountered in kitchen, bath and other home and industrial usage, as Well as the provision of a variety of articles of outdoor use, notably automobile trim, wheel covers, bumpers and like bright metal arts appealing to the eye, yet functional, and well adapted to withstand the conditions encountered in actual practical use such as the dust and heat of summer, the cold of winter and the snow, sleet, ice and salt thrown up from the road in winter driving, as well as the salt atmosphere of the seashore, all without objectionable pitting, corrosion, rusting and discoloration.

Other objects of my invention will be apparent, or will be pointed to, during the course of the description of my invention which follows.

Accordingly, my invention will be seen to reside in the combination .of elements, the composition of ingredients and the relation between the same, and in the products and articles of use embracing the same, all as described herein, the scope of the application of which is set forth in the claims at the end of this specification.

Now in order to gain a better understanding of certain features of my invention, it may be noted at this point that the well known type 430 stainless steel (analyzing carbon .12% max., maganese 1.00% max., silicon 1.00% max, phosphorus .04% max., sulphur 03% max., chromium 14.00% to 18.00%, and remainder iron) has been well received in the art. Cold-rolled and annealed sheet and strip of the type 430 steel has a tensile strength of about 75,000 p.s.i., a yield strength of about 45,000 p.s.i., an elongation in 2" of about 25%, and a hardness of about Rockwell B80. While this steel lends itself to common working and forming operations, the corrosionresisting characteristics of the metal leave much to be desired..

In the automotive industry the type 430 was widely employed in bright metal parts. Under severe weather conditions encountered in actual use, however, these bright metal parts lost their lustre, became pitted and were subject to the development of a red rust. And the eye appeal of bright metal was quickly lost and the general appearance of the automobile immediately suffered. The automotive industry turned to other metals.

Aluminum and its various alloys, while oifering promise, lacked the hardness and strength necessary. The metal in the form of automobile body trim was easily dented and appearance suffered as a consequence. Moreover, the metal lacked lustre and generally left much to be desired.

Now the type 301 grade of stainless steel (analyzing carbon 0.15% max., manganese 2.00% max, silicon 1.00% max., phosphorus .045 max., sulphur .03% max., chromium 16.00% to 18.00%, nickel 6.00% to 8.00%, and remainder iron) has been rather well received in the art for a variety of applications. The same may be said for the type 302 (analyzing carbon 0.15% max., manganese 2.00% max., silicon 1.00% max., phosphorus .045% max., sulphur .03% max., chromium 17.00% to 19.00%, nickel 8.00% to 10.00%, and remainder iron).

Cold-rolled sheet and strip of the type 301 steel in annealed condition has a tensile strength of about 110,000 p.s.i., a yield strength of about 40,000 p.s.i., a 2" elongation of about 60%, with a hardness of about Rockwell B85. The type 302 cold-rolled and annealed sheet and strip has a tensile strength of about 90,000 p.s.i., a yield strength of about 40,000 p.s.i., a 2" elongation of about 50%, and a hardness of about Rockwell B85. 7 Although the type 301 steel is workable and formable, it nevertheless is costly to convert from hot-rolled strip to thin flat-rolled products, this largely as a result of an inherent high work-hardening characteristic. In a coldrolling operation, intermediate annealing of the metal becomes necessary as a result of the development of hardness values unacceptable for further working. Such intermediate annealing is both time-consuming and costly, particularly in that it interrupts progress of the conversion operation. The type 302, although of low workhardening rate, is somewhat more expensive than the type 301.

A further known steel is the chromium-nickel-copper steel as described, for example, in the Bloom-Clarke U.S. Letters Patent 2,687,955 of August 31, 1954, entitled, Cold-Workable Stainless Steel and Articles. While that steel possesses a comparatively low work-hardening rate it, too, is comparatively expensive. And, moreover, at the higher nickel levels, when subjected to drastic deformation, as in severe deep-drawing in a single operation, the steel is inclined to local stressing and resultant irregularity in section.

Accordingly, one of the principal objects of the present invention is the provision of a stainless steel of desired corrosion-resisting characteristics which employs a minimum of expensive alloying ingredients in its composition; which handles well in the furnace and teeming ladle; which works down from ingot to billet to sheet, strip, wire and the like, with ease; and which then readily lends itself to cold-reduction up to some to without necessity for intermediate anneal as in the production of cold-rolled sheet, strip and cold-drawn wire; which sheet, strip and wire are ductile and readily formable by a variety of forming operations.

Referring now more particularly to the practice of my invention, I provide a stainless steel which possesses the corrosion-resisting characteristics of the types 301 and 302 steels at substantially lower cost of converted products, that is, hot-rolled sheet, strip, wire and the like, as

well as cold-rolled sheet, strip, wire, and other coldworked products. There is a savings in ingot costs as compared to type 302, deriving from a saving in the cost of alloying ingredients. And, as compared to the type 301, there is a savings in the cost of conversion deriving from a shorter routing of the metal through the mill, this being permitted because of a lowering of the work-hardening rate which characterizes the type 301.

The steel of my invention essentially consists of carbon up to .15 preferably in the amount of about .04% to .15 manganese in the amount of .40% to 2.00%, silicon in the amount of .l5% to 1.0%, chromium in the amount of 16.0% to 19.0%, nickel in the amount of 5.5% to 8.0%, copper in the amount of .5% to 3.5%, nitrogen residual and remainder essentially iron. The steel of my invention is in every sense critical in its composition for I find that with any substantial change in the balance of the ingredients of the composition one or more of the desired properties are lost.

As to the carbon content of my steel, I find that the .15% figure approaches the limit of solubility for normal annealing and cooling rates. A carbon content exceeding .15% is inclined to give a sensitized structure with risk of a severe loss of corrosion resistance. The carbon content preferably, however, is maintained at a value not exceeding .08% in order to assure a minimum of work-hardening and especially a value of .04% to .08% since at least .04% carbon is desired for its stabilizing effect. A preferred range is .05 to 08%.

The manganese content of my steel similarly is critical in that I find a manganese content exceeding 2.00% gives little benefit and increases the cost as well. The manganese content, therefore, amounts to .4% to 2.00%, or even about .5 to 2.00%, and more particularly about 1.25% to 1.75%.

The silicon content of my steel is critical; at least .15 is necessary to assure an ease of furnacing and teeming, while silicon exceeding 1.00% is objectionable because of its ferrite-forming tendencies. An excess of silicon requires additional nickel at, of course, additional expense, to compensate for the same. I therefore employ a silicon content of .15 to 1.00%, this preferably amounting to about .40% to .75

In the steel of my invention the chromium content amounts to 16.0% to 19.0%, this being critical, too. Preferably, this ranges from 16.0% to 18.0%. A chromium content lower than 16.0% results in a loss of corrosion-resistance and, moreover, it is inclined to result in an objectionable increase in the work-hardening rate of the metal. Achromium content in excess of 19.0% is not acceptable because it results in an excessive deltaferrite content at ingot-rolling temperatures. Desired results are had with a chromium content of 17.25% to A nickel content of 5.5 to 8.0% is required in my steel, this preferably amounting to about 6.0% to 8.0%. With a nickel content short of about 5.5% the work-hardening rate becomes excessive and in addition, there is an inclination to develop delta-ferrite. With a nickel content exceeding 8.0% the cost becomes prohibitive. A nickel range of 6.25% to 6.75% gives best results.

Copper is an ingredient essential to the steel of my invention. This is employed in the amount of .5% to 3.5%. Actually, I employ a copper content of about 1.0% to 3.5%, more preferably about 1.0% to 3.0%. A copper content short of the 1.0% figure and certainly anything short of the .5 figure does not elfectively lower the work-hardening rate of the metal. And a copper content exceeding 3.0%, and certainly one exceeding 3.5%, is likely to result in hot-rolling difficulties, notably the likelihood of the metal to break in the hot-mill, since 3.5% is about the limit of solubility. Moreover, I feel that with an excess of copper, the corrosion resistance of the steel is inclined to suifer. The preferred copper range is 1.75% to 2.25%.

In the melting of my steel an electric arc furnace commonly is employed. Where desired, however, it will be understood that the steel may be vacuum melted or otherwise melted to specification. However melted, the steel handles well in the furnace and in the pouring ladle. The steel in the form of ingots is converted into slabs, blooms and billets. It is then reheated and hot-rolled into sheet, strip, wire and the like. The steel works Well in the hot mill.

Conveniently, the hot-rolled metal comes 011 the mill in coils which may be annealed and pickled, or merely pickled and then cold-worked to specification. Cold-rolled sheet and strip is had through a short routing through the mill, that is, without necessity for intermediate anneal. The amount of cold-reduction commonly approaches Similarly, the hot-rolled wire is cold-drawn. And here again, the drawing operation is simply and inexpensively effected without necessity for intermediate anneal, the amount of cold-reduction being up to about 75%.

While all of the many beneficial characteristics of the steel of my companion application are fully enjoyed only with the presence of nitrogen in the amount of .04% to .10% as previously indicated, certain of these characteristics nevertheless are had in the steel of the present invention Where nitrogen is present only in the amount of .03%, or .02%, or .01%, or other residual amount. In the present steel, however, there is observed a significantly greater work-hardening rate, with somewhat greater hardness and tensile strength in the cold-worked condition. But in contrast to that disadvantage, the present steel has less initial hardness and consequently processes a bit easier in the mill. My steel may be viewed as essentially consisting of carbon up to about .l5%, manganese .5% to 2.00%, silicon, .15% to 1.00%, chromium 16.0% to 19.0%, the chromium preferably being 16.0% to 18.0%, nickel 6.5% to 7.9%, copper 1.5% to 2.9%, more especially 1.9% to 2.9%, with nitrogen preferably in residual amounts only, and remainder essentially iron. pecially, such modified steel may be considered as essentially consisting of carbon about .05 to .15 manganese about 1.25 to 1.75 silicon about .40% to .75 chromium 16.0% to 18.0%, nickel about 7.0% to 7.9%, copper about 2.5% to 2.9%, and the remainder essentially iron. In these steels the phosphorus and sulphur contents are in but residual amounts, the phosphorus not exceeding .04% and the sulphur not exceeding .03%, the phosphorus and sulphur contents usually not exceeding about .015 each. Best bend properties are had where the sulphur content does not exceed 006% As specific examples of my present steel, the chemical composition of nine such steels are set out below in Table I:

TABLE I.CHEMICAL COMPOSITION OF NINE STEELE Heat No. 0 Mn P S St Cr Ni Cu N More es- The mechanical properties of the nine steels of Table I in the form of cold-rolled strip, with rolling temperature maintained at about 160 F., are given below in Table II:

TABLE II.MECHANICAL PROPERTIES OF STEELS OF TABLE I IN THE FORM OF STRIP WITH REDUCTION AND WHEN COLD-REDUCED 75%.

Percent .2% Ten. Percent Rockwell Heat N0. Cold- Y.S., Str., Elong. Hardness Reduction K s.i. K s.i. in 2 3611-1 0. 0 36. 7 92.0 64. 73. 0B 74. 4 178. 5 200. 2 1. 5 42. 5 3611-2 0. 0 36. 7 90. 9 58. 0 72. 0B 74. 1 164. 9 194. 0 1.0 41. 0 3611-3 0. 0 36. 7 89. 3 55. 5 74. 5B 74.9 164.8 194. 6 2. 0 41.5 3612-1 0. 0 36. 2 88. 4 60. 5 74. 0B 73. 8 171. 9 195. 6 l 42. 5 3612-2 0. 0 37. 0 88.6 54. 0 73. 513 74.2 166. 2 192. 5 1. 0 41.0 3612-3 0.0 33. 7 85.1 57. 5 71. 5B 74. 9 157. 2 189. 4 2. 0 41.0 3613-1 0. 0 35. 2 86. 5 59. 5 73. 0B 74.7 168. 4 193. 5 2. 0 41.0 3613-2 0. 0 34. 7 35'. 6 56. 0 72. DE 74.9 164. 8 189. 4 2. 0 40.0 3613-3 0.0 33. 9 84. 9 56. 0 72. 5B 75. 0 154. 8 181. 8 2. 0 40. 0

Of the steels set out above, the low nitrogen steel of Heat 3611-1 may be compared with the high nitrogen steel of the heat M3 of my companion application (057% carbon, 1.64% manganese, .50% silicon, 17.61% chromium, 7.00% nickel, 1.98% copper, 030% nitrogen, remainder iron, for the Heat 3611-1, and 064% carbon, 1.49% manganese, .43% silicon, 17.74% chromium, 6.47% nickel, 1.93% copper, 060% nitrogen, and remainder iron, for the Heat M3). These two steel are of about the same carbon, manganese, chromium, nickel and copper contents. While the steel of Heat M3 when coldreduced about 75% (75.7% cold-reduction) has a .2% Y.S. of 176.6 kilo pounds per square inch anda tensile strength of 192.2K s.i., the steel of Heat 3611-1, when similarly cold-reduced (74.4% cold-reduction) has a .2% yield strength of 1785K s.i. and a tensile strength of 2002K s.i. The increased tensile strength had as a result of cold-reduction amounts to 1082K s.i. for the steel of Heat 3611-1 (920K s.i. for 0% cold-reduction and 2000K s.i. when cold-reduced about 75%) as against an increase of only 96.3K s.i. for the Heat M3 (95.9K s.i. for 0% cold-reduction and 192.2K s.i. when cold-reduced about 75% As a further example, the steel of Heat 3612-1 of low nitrogen content (055% carbon, 1.55% manganese, .42% silicon, 17.63% chromium, 6.96% nickel, 2.49% copper, 031% nitrogen, and remainder iron) when coldreduced 75% (73.8% cold-reduction) has a .2% yield strength of 171.9K s.i. and a tensile strength of 195.6K s.i. as against a .2% yield strength of 173.5K s.i. and a tensile strength of 191.7K s.i. for the high nitrogen steel of Heat F3 of my companion application (068% carbon, 1.64% manganese, .48% silicon, 17.82% chromium, 6.96% nickel, 2.40% copper, 090% nitrogen, and remainder iron) when cold-reduced about 75 (73.3% cold-reduction). It is noted that While the increase in tensile strength of the steel of Heat 3612-1 as a result of cold-reduction comes to 1072K s.i. (88.4K s.i. for 0% cold-reduction and 195.6K s.i. for the 75% reduction), the increase in tensile strength for the steel first described, F3, amounts to 990K s.i. (92.7K s.i. for 0% cold-reduction and 191.7 for the 75% reduction).

In both of the illustrative examples of my present steel it is note-d that while the work-hardening rate is somewhat greater than for the steels first described, the initial strength, that is, in the annealed condition and 0% cold-reduction, is somewhat lower (920K s.i. for Heat 3611-1 as compared to 959K s.i. for Heat M3, and 88.4K s.i. for Heat 3612-1 as compared to 92.7 for Heat F3). Compare also my low nitrogen high copper steel Heat 3611-1 (057% carbon, 1.64% manganese, 50% silicon, 17.61% chromium, 7.00% nickel, 1.98% copper, .030% nitrogen, and remainder iron), having a tensile strength in the annealed condition of 920K s.i., with the steel of like composition but free of copper, Heat D1 of my companion application (066% carbon, 1.03% manganese, 50% silicon, 17.76% chromium, 7.65% nickel, .15 copper, 046% nitrogen and remainder iron) which has a tensile strength of 117.6K s.i. The lower initial tensile strength of my present copperbearing steel makes for easier working, as also does the lower work-hardening rate (108.2K s.i. increase with 75 cold-reduction for Heat 3611-1 as against 1223K s.i. increase for Heat D1). Both factors are in favor of the copper-bearing steel of low nitrogen content.

Thus it will be seen that I provide in my invention a stainless steel of good corrosion-resisting characteristics, employing a minimum of expensive alloying ingredients. The steel is economically melted in the electric arc furnace. It furnaces well and teems well. Moreover, because of its comparatively low work-hardening rate, this as compared to the well known type 301 chromium-nickel stainless steel and a variety of other chromium-nickel steels, the steel of my invention may be cold-worked, as by cold-rolling or cold-drawing, to a reduction in area amounting to about 75 or more without requiring an in termediate annealing operation. The production of coldrolled sheet and strip, and cold-drawn wire from hotrolled sheet, strip and wire thus is achieved at minimum expense.

The steel and sheet, strip, wire and the like of my invention conveniently is supplied the trade in an annealed and pickled or in a bright annealed condition at significantly lower cost. These mill products well lend themselves to fabrication, as by bending, drawing, deep-drawing and other forming operations commonly practiced on the well known 18-8 chromium-nickel grade of stainless steel. Moreover, these products may be sheared, cut, sawed, drilled and the like, as well as brazed and welded, as in the production of a variety of articles of ultimate use such as automobile body trim, window frames, door frames, wheel covers, bumpers, and the like, where bright metal and appeal to the eye is desired. The steel and articles well resist the attack of the salty atmosphere encountered at the seashore as well as the salt thrown up from the streets, roads and highways during the winter when salt commonly is employed to effect de-icing. And the steel of my invention is well adapted to withstand the abuse commonly encountered in every-day automobile driving and parking.

Other articles of ultimate use fashioned of my steel include kitchen sinks, kitchen and bathroom fittings, trim, and the like, where corrosion-resistance and eye appeal are required. The steel is well calculated to resist the attack of various mild acids, bases and salts encountered in a number of commercial and industrial uses.

Many embodiments of my invention will occur to those skilled in the art to which the invention relates, and many variations will occur with respect to the embodiments herein disclosed. Therefore it will be understood that all such matter described herein is merely illustrative; it is not to be taken as a limitation.

I claim as my invention:

1. Stainless steel essentially consisting of carbon up to about .15%, manganese .5% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 19.0%, nickel 6.5% to 7.9%, copper 1.5% to 2.9%, residual nitrogen, and remainder essentially iron.

2. Stainless steel essentially consisting of carbon about .05% to .15%, manganese about 1.25% to 1.75%, silicon 7 about .15% to 1.00% silicon, about 16.0% to 19.0% chromium, about 6.5% to 7.9% nickel, about 1.5% to 2.9% copper, residual nitrogen, and remainder essentially iron.

4. Stainless steel having good bend characteristics essentially consisting of carbon up to about .15 manganese .5 to 2.00%, sulphur not exceeding 006%, silicon .15 to 1.00%, chromium 16.0% to 19.0%, nickel 6.5% to 7.9%, copper 1.5% to 2.9%, nitrogen up to .O3%, and remainder essentially iron.

5. Hot-rolled chromium-nickel-co-pper stainless steel sheet, strip, wire and the like essentially consisting of carbon up to about .15%, manganese .5% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 19.0%, nickel 6.5% to 7.9%, copper 1.5% to 2.9%, nitrogen up to .03 and remainderessentially iron.

6. Cold-rolled chromium-nickel-copper stainless steel sheet, strip and like products essentially consisting of carbon up to about .15%, manganese .5% to 2.00%,

2O silicon 15% to 1.00%, chromium 16.% to 19.0%,

8 nickel 6.5% to 7.9%, copper 1.5% to 2.9%, nitrogen up to .03 and remainder essentially iron.

7. Cold-rolled chromium-nickel-copper stainless steel sheet, strip and like products having good bend characteristics essentially consisting of carbon up to about .15 manganese .5 to 2.00%, sulphur not exceeding 006%, silicon .15% to 1.00%, chromium 16.0% to 19.0%, nickel 6.5% to 7.9%, copper 1.5% to 2.9%, residual nitrogen, and remainder essentially iron.

References Cited by the Examiner UNITED STATES PATENTS 2,150,901 3/1939 Arness 75128 2,482,098 9/1949 Clark 75-125 2,687,955 8/1954 Bloom 75125 2,784,125 3/1957 Clark 75-128 X 3,183,081 5/1965 Clark 75-125 HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, P. WEINSTEIN, Assistant Examiners. 

1. STAINLESS STEEL ESSENTIALLY CONSISTING OF CARBON UP TO ABOUT .15%, MANGANESE .5% TO 2.00%, SILICON .15% TO 1.00%, CHROMIUM 16.0% TO 19.0%, NICKEL 6.5% TO 7.9%, COPPER 1.5% TO 2.9%, RESIDUAL NITROGEN, AND REMAINDER ESSENTIALLY IRON. 